Vehicle headlight



Jan. 13, 1931. w. H. woon v 1,788,934

' VEHICLE HEADLIGHT Filed Jan. 24, 1923 2 Sheets-Sheet 1 IN VEN TOR.

'- William H.W00d- BY ,wmmzz ATTORNEY.

Jan. 13, 1931. w. H. WOOD VEHICLE HEADLIGHT Filed Jan. 24,1923 2Sheets-Sheet 2 FRY.

INVENTOR.

ATTOARNEY. W

Patented Jan. ,13, 1931 UNITED STATES WILLIAM H. WOOD, OF CLEVELAND,OHIO VEHICLE HEADLIGHT application filed January 24, 1923. Serial No.614,694.

This invention relates to vehicle headlights and has for its object theprovision of a simple and easily made sheet metal reflector which shallproduce a legally acceptable and practically satisfactory distributionof light without the use of lenses, prisms, shades, dimmers or otherexpensive, fragile, or light killing devices. The present and prospective legislation of thedifi'erent States and municipalities requires alllight rays to be kept below a certain fixed angle while affording aminimum strength of beam in other regions slightly below the horizontal,while the requirements of easy driving necessitate a restriction of theintensity at points near the vehicle in order to increase the visibilityof objects at a greater distance ahead of the vehicle. These twoconsiderations practically require a concentration of the reflected raysinside a rectangular or elliptical space whose major dimension ishorizontal. addition it is desirable that the adjustment requirements benot unduly exact or sensitive, both to facilitate its use by unskilled 5persons and to minimize the difficulty occasioned by accidental changein adjustment. A plain paraboloid reflector is inadequate to producethese results, both because of the straying of some portions of thelight beam and the streaky character of otherportions, as well as theimpossibility of securing this distribution except by the assistance ofexpensive and fragile lenses. It is possible to secure a measurablysatisfactor character of light distribution by the use 0 a combinationof paraboloid segments, although the focussing requirements aresometimes unduly exact and it is difficult to join the differentsegments in a smooth manner so as to enable easy polishing. Combinationsof flat surfaces and of corrugated surfaces have also been attempted,but these are diflicult to make and are even more difficult to-repolishin case of need.

I have now discovered a new, mathematically-definite surface so locatedrelatively to the light source as effectually to control all parts ofthe light beam with a hi h degree of exactness, and likewise devoid 0all sharp angles, edges, or corrugations, thus enabling readymanufacture L and easy renovation.

Another feature of my improved surface is that the character of thelight beam thrown thereby is almost entirely independent of the shape orsize (within comparatively broad limits) of the light source or itslongitudinal position inside the reflector.

In the drawings accompanying and forming apart of this application Ihave illustrated the mode of generating my improved reflector surfacetogether with a finished reflector embodying the same. In these drawingsFig. 1 is a diagram showin the mode of generating a true parabola; Tig.2 is a similar view showing the mode of generate in'g'my improved curveas employed for the top of my reflector; Fig. 3 shows the mode ofgenerating the curve emplo ed for the bottom of the reflector; Fig. 4 1sa vertical sectional view of the reflector showing the relative positionof the two segments; Fig. 5 is a face View of the reflector showing themode of connecting the segments together; Fig. 6 is a View of the lightpattern as thrown on a vertical, screen; Figs.- 7, 8, 9, and 10 arediagrammatic views showing the reflector segments assembled togetherwith different relative positions of the points S and S together withthe position of the light source relative-thereto.

In Fig. 1, AA is the geometrical axis,

. D-D the directrix, V the vertex, and f the focal point of theparabolaA, the nature of the parabolic curve being such that every point of thesame 'is equally distant from the focal point and from the directrixwhich is a straight line. Therefore fv=ow fb=bb fczcc fdzdd Inasmuch asno known practical source even approximates the size of a geometricalpoint a true paraboloid produces reflected rays of all kinds even wherethe source is focussed as accurately as possible; indeed a single pointsource if displaced from the axis will itself produce all kinds of rayssince the direct rays which fall behind the parameter are converged asseeming to originate from forward of the focal point and those whichimpinge forward of the param-- eter are diverged as seeming to originatebehind the focal point.

The essenceof my invention resides in displacing the focal pointvertically from the axis and then correcting every point of the curve tocompensate for this displacement. To do this I draw a line 1-1 torepresent the horizontal geometrical or :n-axis and above it I locatedthe point 8, say ,4; inch therefrom. Through this point I draw avertical line two inches long touching the axis at 2. This linecorresponds to the parameter of "a parabola and the upper end 3 of thisline is a pointof the curve at which its inclination to the axis 1- -1is exactly 45. Also at a point in the rear of the line 23 I draw aparallel line D-D', at the same distance from the point 3 as 3 isdistant from 2. Thus far the procedure conforms exactly to that followedin drawing a true parabola, symmetrical about the horizontal or :v-axiswith its vertex tangent to the y-axis.

I now draw an inclined line through the point S soas to intersect boththe axis 11 and-the probable curve, say the line e intersecting the axisat 4. I then draw a perpendicular E E the same distance behind the lineD D that4 lies in front of 2, and on the line 6 locate the point 5 whichis equidistant from the line E E and the intersection 4.

I then draw another inclined line 9 through the oint S'intersecting theaxis at 6, and also raw a corresponding directrix G G as far behind D Das the point 6 lies in front of the point 2. On this line 9 I then findthe point 7 which is equidistant from the point 6 and from the line G G.I repeat the same performance for a suflicient number of other lines, h,2' (etc.) to locate other points 8, 9, 10, 11 -(etc.) arid plat anaccurate curve between the parameter and the vertex.

I then draw an inclined line 9' through the point S intersecting theaxis at- 12 between the parameter and the vertex and to accompany it Idraw a perpendicularJ J as far in front of the line D D as 12 is distantfrom 2, after which I find the point 13 on this line equidistant fromthe oint 12 and the line J J This is repeate for the lines lo and K Kgiving the points 14,15 and as manyother times as desired, afterwhich acurve Y is drawn connecting the points 3, 5; 7, 9, 13, 15. This curve isrestricted to the re on above the line 1-1.

o secon line 20-20 as in Fig. 3 and lace at inch above it a point S fromWhlCh I drop a perpendicular intersecting the axis at 21;'and on thisline at about 2 inches,

' (more or less,' but preferably a little more than the distance 2-3 fora'reason to be explained hereafter) I locate the point 22 which is apointon the curve; also below lat the line below the axis I draw a I,point 22 shall be equidistant from 21 and from P P.

I then draw an inclined line g through the point S intersecting the axisat 23 behind the point 21 and I also draw a second perpendicular Q Q thesame distance in front ofP P as 23 is behind 21. On this line I thenlocate the point 24 equidistant from the point 23 and from the line Q Q.After repeating this with other lines 1', t, etc. to find the points 26,28, etc., sufiicient innumber to produce an'accurate curve, I draw otherlines as u intersecting the axis at 29 in front of the point 21 and foreach I draw a corresponding perpendicular as U U an equal distancebehind the line P P, thus finding the points 30, 32, etc. in the samefashion; I then connect the points 22, 24, 26, 28, 30, 32 producing thecurve Z.

I then rotate each curve perpendicular to its plane, the curve Y aboutthe axis 1-1 and the curve Z about the axis 2020, to form a partialsurface of revolution and I assemble these together as shown in Fig. 4with their axes coinciding and'the points S, S spaced longitudinallyapart, with the point S at the rear. If the distance 21--22 was properlychosen relative to the distance 2-3, the vertices of the two curves willmatch properly with the desired longitudinal separation of thesepointssay inch. Also the forward end of the lower segment is slightlywider than thatof the upper segment enabling the two to be joined at thesides by wing portions X X as described and wide at the front andtapering rapidly rearwardly asthis produces a better placingof thereflected rays and also' enables, the smooth joining of the differentsegmentsl The heel ofthe reflector is formedJWith a socket-hole W inline with the points S, S

and the light SO lIICQ WhlCh is generally an electric light filament islocated between these two points, the reflector being leaned rearwardlya slight amount so, as to elevate the axis 1-1 above the horizontal, butwithout elevatin the reflected rays above tlie horizontal. ration of thetwo points S, S. y

The lamp filament is indicated at L. In the case of the usual paraboloidreflector the effect of elevating the light source above the axis wouldbe to cause all rays striking the reflector as if originating ahead ofthe parameter to be converged and those striking is compensates for thesepathe reflector as if originating behind the parameter to bediverged,thus creating an up wardly converging glare from thellower fo ralong theaxis.

to spread them horizontally.

light source be located either forward of S or rearward of S and bymaking the distance between these at least as great as the length of thelargest commercial filament a lamp is produced which ispeculiarlyinsensitive to focussing. Each ray of light falling on any part of thevertical zone has the same effect as though it came from a point on theaxis at some distance beyond the point S, or at some nearer point withinthe point S, these points accordingly constituting what might be calledvirtual foci and these virtual foci are progressively spaced along theaxis. The curve can be considered as a compound parabola wherein thefoci of successive segments are progressively displaced Also this sameadjustment of the curve for the vertical displacement removessensitiveness in all other respects and further produces exactly thepattern of light beam desired, namely an oblong field, since the samecorrection which serves to compress the rays in a vertical plane servesLikewise every part of the field is illuminated at all times bydiverging rays from one part of the reflector and by converging raysfrom another part thereof, thus producing a uniform, difiusedillumination; and if by minor variations in the position of the lampfilament one setof rays should be weakened, the effect of another set ofrays will be strengthened, thereby keeping all parts of the fieldilluminated to substantially the same degree unless the focussing limitsbe exceeded. Owing to the occurrenceof this action in three dimensionsit is possible to illustrate the path of these rays only in the verticalplane since all other regions of the reflector are subjected to 'a crossfire of rays and the path of the reflected ray is seldom or never in thesame plane with that of the incident ray.

It will be obvious that any light source of infinitely small sizelocated exactly on either point S or S will have its reflected rays sentforward parallel to the axis 11 and that if it be moved to the rear ofthe point S all rays reflected by the segment Z will be deflected belowthe axis 1- 1. Likeover a considerable range of adjustment.

This same result is achieved simultaneously by the separation of the twopoints S and S, the light source remaining between them. and thesuperposed beams are deflected downwardly past the axis so that it isdesirable to incline this axis upwardly to prevent the light strikingthe ground too near the vehicle. See Fig. 7.

It may be noted, however, that it is perfectly feasible to locate thepoint S ahead of the point S and compensate for the resulting upwarddeflection of the com ound beam by a downward inclinationof t ereflector axis as shown inFig. 8.'

Furthermore it is possible by inclining the axes of the respectiveportions Y and Z to obtainthe same optical results as by an axialshifting of the points S, S Thus if the lower segment be tippeddownwardly as shown in Fig. 9 the same optical result is obtained as bythe arrangement shown in Fig. 4, the light source being located ahead ofthese points. Likewise if the upper segment be tipped downwardly asshown in that in my drawings I have greatly exaggerated the elevationand separation of the points S, S as compared to the parametral radiusof the curve. This particular curve is mathematically known as a cubicand when accurately made is defined by the equation wherein p representsthe abcissa and c the ordinate of the point S or S; The heel portion ofthis curve is practically indistiguishable from the heel portion of aparabola whose focal point coincides with S or S and Whose vertex fallson the cubic and whose axis is inclined to the m-axis at an obliqueangle whose abruptness increases with increase of 0 relative to 17,being zero when 0 equals zero. The points S, S exhibit many of thecharacteristics of a focal point.

According to another point of view the portions of the curve above thecenter of the reflector may be referred to the reflector axis as amodified semi-parabola in which the focal length increases from the limbtoward the vertex in such a manner that all focal lines passsubstantially through a selected point located above such axis, whichpoint thus becomes the virtual focus of such curve; whilerthe portionthereof below the center of the reflector may be considered as amodified semi-parabola in which the focal length decreases from the limbtoward the vertex in such a manner that all focal lines passsubstantially through a selected point also located above the reflectoraxis. These curves, in whichever way they be" defined,

are employed as generators for defining the reflector surface, or atleast that part of the same lying at and near the central longitudinalvertical plane; and conversely the reflector surface whose intersectionwith a verticalfaxial plane exhibits the curves herein defined containsthe invention which it is my purpose to claim and secure.

- I have illustrated in detail only the type in-which the source iselevated above the geometrical, axis, but it will be apparent that thesame adjustment can readily be made for a source located beneath theaxis and the resulting curve built into a reflector. Such a deviceexhibits no advantages over the one herein illustrated and contains thedefect that the two halves do not. match each other so well and are more'diflicult to join.

, tions integrally connected together.. Such a reflector exhibits aslightly oval front but contains no corrugations, sharp angles, orreentrant' surfaces and can be plated and polished bymachine methods aseasily as a plain paraboloid.

The essence of this invention resides in my new curve and the mode ofcompensating by theone act for; all variations en.- countered in headliht practice, but I do not limit myself to t e particular method oflaying out the curve hereii before described since the same substantialgenerator by whatever mathematical or drafting process it be identifiedfalls within the purview of my invention, and I do 'notlimit myself asregards the angular extent of the generator employed or the angularextent ofthe rotation of such generator about any axis of revolutionexcept asspecifically recited 'in my several claims. 7

Having thus described my invention what I claim is: 1

1. In a headlight, a reflector having its upper portion conforming to asurface of revolution about a substantially horizontal axis of agenerator whichhas for a focus a point which is displaced above the axisof revolution, and having its lower portion also conforming to'a surfaceof revolution about a substantially horizontal axis of a? secondgenerator which has for a focus a point which is displaced from thegeometrical axis of said second generator, said two axes of revolutionbeing located in the same vertical lane. 2; n a headlight, a reflectorhaving above its central horizontal plane a surface demy signature.

fined substantially by the transverse movement of a generator whichconsists of a modified semi-parabola whose focal length constantlyincreases from its forward limb to its vertex in such a manner that allfocal lines pass substantially through a selected of a modifiedsemi-parabola whose focal length constantly decreases from its forwardedge to its vertex'in such a manner thatall focal lines pass through aselected point above the parabolic axis, which point thus becomes thevirtual focus of the generating curve in said vertical plane. Y

4. In a headlight, a reflector whose uppermost segment consists of asurface substantially defined by the transverse movement of a generatorwhich consists essentially of a modified semi-parabola whose focallength increases from its forward limb toward its vertex, and whoselowermost segment consists of a surface substantially defined by thetransverse movement of a different generator which consists essentiallyofa modified, semi-parabola whose focal length decreases from itsforward limb to ward its vertex, the focal lines of each generatorpassing substantially through a selected point above the correspondingparabolic axis which point thus becomes a vir tual focus for itsrespective generator.

5. A headlight having the portion of its reflector directly above itsaxis substantiallyl defined by a curve which is essentially a modifiedsemi-parabola whose focal len h constantly increases from its forward ego toward its vertex in such a manner that all focal lines pass througha selected point above the parabolic axis, which point thus becomes thevirtual focus of the curve; and having the portion of its reflectordirectly below its axis definedby a curve which is essentially anothermodified semi-parabola whose focal length decreases. constantly from itsforward edge to its vertex in such a manner that all focal lines passthrough a selected vpoint above such second parabolic axis which pointthus becomes the virtual focus of such lower curve, both of said pointsand both of said virtual foci being located in the same vertical plane,a light source located above both parabolic axes and the two sides ofsaid reflector being closed by portions whose normals all pass belowsaid light source. 4

In testimony whereof, I hereunto afl'ix WILLIAM H. WOOD.

